A human transforming gene, dbl, was isolated from the DNA of a primary human diffuse B-cell lymphoma by the DNA transfection assay on NIH/3T3 cells. This human oncogene was cloned in a biologically active form in a cosmid vector as a human DNA sequence of 4.5 kilobases. By hybridization studies between cellular and viral oncogenes and their cloned human transforming gene, dbl was shown to be unrelated to any previously reported oncogenes. A cDNA library was constructed in GammaGT11 with polyadenylated RNA purified from a dbl third-cycle transfectant. Several clones were isolated and their structure and nucleotide sequence are now being analyzed. Using sera obtained from mice bearing tumors induced by dbl transfectant, a 66,000 dalton protein (p66) was specifically detected in dbl-transformed NIH/3T3 cells. This protein was found to be the translational product of dbl oncogene. Moreover, preliminary subcellular localization studies reveal that p66 was distributed between cytosol and crude membrane fraction, p66 could be phosphorylated in vivo, and phosphoserine appears to be the only detectable phosphoamino acid residue on p66 protein. We had earlier analyzed, by transfection assay, DNAs of two groups of MCA-induced fibrosarcomas in BALB and NIH Swiss mice for their ability to transform NIH/3T3 cells and found that an activated K-ras was detectable in 50% of the tumor DNAs analyzed. Cell lines were established from one of the two groups of tumors and analyzed for their growth capability in vivo. Results obtained so far seem to indicate that the presence of an activated K-ras gene is associated with strikingly faster growth of the tumor cells in vivo as compared with the growth of MCA tumor cells that do not contain an activated ras gene.